JP2001085330A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce stress induced in a polycrystalline semiconductor to an irreducible minimum in a thermal recrystallization process by a method wherein a non-single crystal semiconductor is provided on a glass substrate which is thermally treated at a lower temperature than a distortion point and then turned polycrystalline by heating. SOLUTION: A glass substrate 1 (AN-2 non-alkali glass) is thermally treated for 12 hours at a temperature of 610 deg.C lower than its distortion point. The thermal treatment is carried out in an atmosphere of inert gas (N2) under an atmospheric pressure by the use of an electric oven. When the treatment is carried out in an atmosphere of inert gas loaded with hydrogen under an atmospheric pressure or a reduced pressure, the substrate can be cleaned at the same time. Then, an SiO2 film 2 is formed, for instance, as thick as 200 nm through an RF sputtering method. An a-Si active layer 3 is deposited thereon, for instance, as thick as 100 nm through RF sputtering method. Thereafter, the a-Si active layer 3 is thermally recrystallized at a temperature of 600 deg.C for 96 hours in an atmosphere of nitrogen. A thermal recrystallization process is carried out in an electric oven in an inert gas atmosphere under an atmospheric pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for thermally recrystallizing a non-single-crystal semiconductor to obtain a polycrystalline semiconductor.

[0002]

2. Description of the Related Art A technique for obtaining a polycrystalline semiconductor by thermally recrystallizing an amorphous silicon semiconductor obtained by a gas phase chemical reaction method or a sputtering method is known.

[0003]

When a polycrystalline semiconductor is obtained by thermally recrystallizing an amorphous silicon semiconductor obtained by a gas phase chemical reaction method or a sputtering method, a substrate is heated at a temperature of about 600 ° C. for a long time. Must.

As the substrate, it is preferable to use an industrially inexpensive glass substrate. However, the temperature around 600 ° C. is the strain point temperature of the glass substrate, and the thin film transistor obtained by thermal recrystallization is used for a large area liquid crystal display device. For example, the following problem occurs due to the shrinkage of the glass substrate. B) Due to shrinkage of the glass substrate in the thermal recrystallization step, the photolithography pattern after this step is deformed, making it difficult to align the mask in the subsequent step. B) Shrinkage of the glass substrate in the thermal recrystallization step generates stress inside the recrystallized polycrystalline semiconductor. It has been experimentally confirmed that this stress adversely affects the electrical characteristics of the polycrystalline semiconductor.

[0005]

An object of the present invention is to reduce the shrinkage of a glass substrate, which is a problem in the step of obtaining a polycrystalline semiconductor by thermally recrystallizing a non-single-crystal semiconductor obtained by a gas phase chemical reaction method or a sputtering method. To solve the problem, and due to the shrinkage of the glass substrate, minimize the occurrence of stress in the polycrystalline semiconductor in the thermal recrystallization step,
It is an object of the present invention to improve the electrical characteristics of a semiconductor device made of a semiconductor provided on this substrate.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a step of heat-treating a glass substrate at a temperature below the strain point of the glass substrate, a step of providing a non-single-crystal semiconductor on the heat-treated glass substrate, A semiconductor manufacturing method including a step of heating a non-single-crystal semiconductor provided over a substrate to polycrystallize the semiconductor.

The heat treatment of the glass substrate at a temperature below its strain point minimizes shrinkage of the glass substrate due to heat applied in the step of polycrystallizing a non-single-crystal semiconductor provided on the glass substrate. This is to improve the electrical characteristics of the semiconductor provided on the glass substrate.

This is because stress is generated in the polycrystalline semiconductor thermally recrystallized on the glass substrate due to the shrinkage of the glass substrate due to the heat applied in the recrystallization. This is based on the experimental fact that an interface state in a polycrystalline semiconductor formed over a substrate is increased and electrical characteristics of the polycrystalline semiconductor are reduced.

The purpose of the heat treatment is to change the properties of the glass substrate against heat by preheating the glass substrate.

Heating in this heat treatment may be performed in an electric furnace in an inert gas at atmospheric pressure. However, when this heat treatment is performed in an atmosphere containing hydrogen, the substrate can be washed at the same time.

Further, the step of thermally recrystallizing a non-single-crystal semiconductor by heating it is performed in an electric furnace in an inert gas at atmospheric pressure.

It is important that the heating in the recrystallization step be performed in an inert gas. This is because it is necessary to prevent the semiconductor from reacting with a gas (eg, oxygen) in the process of thermal recrystallization.

The term "non-single-crystal semiconductor" used herein refers to a non-single-crystal semiconductor in an amorphous state, a semi-amorphous state, and a microcrystalline state, and does not include a polycrystalline state.

The microcrystalline state refers to a state in which a crystalline state is scattered in an amorphous state.

The step of providing a non-single-crystal semiconductor on a heat-treated glass substrate uses a gas phase chemical reaction method, a sputtering method, a vacuum evaporation method, an ion cluster beam method, a molecular beam epitaxy method, a laser ablation method, or the like. This means that a non-single-crystal semiconductor is manufactured.

The strain point of the glass is that the viscosity of the glass is 4 × 10 ¹⁴ p
Defined as the temperature when oise (logη = 14.5).

[0017]

EXAMPLES Example 1 The glass substrate used in this example was Asahi Glass's AN-2 non-alkali glass, and the strain point of this glass was 616 ° C.

First, a heat treatment was performed on the glass substrate at a temperature of 610 ° C. for 12 hours. Although the heat treatment is performed in an electric furnace in an inert gas at atmospheric pressure (N ₂ ), the heat treatment may be performed in an inert gas atmosphere in a reduced pressure state to which hydrogen has been added.

[0019] Next, the Si0 ₂ film by sputtering 200nm
A-Si film on it by PCVD.
The a-Si film was deposited at a thickness of 100 nm and thermally recrystallized at a temperature of 600 ° C. for 96 hours. The thermal recrystallization is performed in an inert gas (N ₂ ) at atmospheric pressure in an electric furnace.

The above is an embodiment of the present invention. Experimental data will be shown below to clarify the effects of the present invention.

First, the results of an experiment for preventing shrinkage of a glass substrate during heating, which is one of the objects of the present invention, will be described.

FIG. 1 shows the glass substrate (AN-2 non-alkali glass) subjected to the heat treatment used in the present embodiment (A) and the glass substrate of the same material without the heat treatment (B).
3 shows the temperature dependence of the shrinkage ratio of the glass.

As is apparent from FIG. 1, the shrinkage of the heat-treated glass substrate (A) is 1/5 or less of the shrinkage of the glass substrate (B) not heat-treated.

Further, it can be seen that the shrinkage has a temperature dependence of the active form, and tends to increase exponentially as the temperature rises.

FIG. 2 shows a glass substrate (AN-2 non-alkali glass) (A) heat-treated at a temperature of 610 ° C. for 12 hours and an untreated glass substrate (AN-2 non-alkali glass). This shows the dependence of the shrinkage rate of the glass on the heating time when the alkali glass (B) is heated at a constant heating temperature of 600 ° C.

As apparent from FIG. 2, the glass shrinkage tends to be the largest for the first few hours, and tends to be saturated as the heating time becomes longer.

When heated for 96 hours, no heat treatment is applied to AN-2
The shrinkage of the non-alkali glass (B) was about 2000 ppm, and the shrinkage of the heat-treated AN-2 non-alkali glass (A) was about 500 ppm.

From the above, it can be understood that the heat treatment of the glass substrate in advance can minimize the shrinkage of the glass substrate due to the heat applied in the step of polycrystallizing the non-single-crystal semiconductor provided on the glass substrate. .

Further, the glass substrate (AN-
The activation energy of (2 non-alkali glass) is about 0.08 eV, corresponding to the transition temperature (668 ° C.) of AN-2 non-alkali glass, which is considered to be related to the properties of the glass.

[0030] to determine the activation energy from the experimental data, using the relational expression _{R = Aexp (-E a / kT} ) is an equation representing a straight line in the graph shown in FIG. A is the proportionality constant, E
_a is the activation energy and k is the Boltzmann constant.

FIG. 3 shows a heat-treated glass according to the present embodiment.
On a substrate (AN-2 non-alkali glass) by sputtering
SiO_TwoA film is formed to a thickness of 200 nm, and a
-Si film is deposited to a thickness of 100nm, and at a temperature of 600 ° C for 96 hours
Semiconductors after thermal recrystallization of a-Si film over a long time (a)
And without performing the heat treatment of the glass substrate in this embodiment,
On this substrate, SiO_Two200nm thick film
After formation, an a-Si film with a thickness of 100 nm is
Deposit to a thickness and spend 96 hours at 600 ° C for a-S
A semiconductor (b) with a thermally recrystallized i-film and a quartz substrate
SiO by putter method _TwoAfter forming the film to a thickness of 200 nm,
A-Si film is deposited on top of it by PCVD to a thickness of 100 nm.
At a temperature of 600 ° C for 96 hours,
The three types of semiconductors (c) that have been crystallized
2 shows the dependence of the Raman spectrum on the substrate.
The relative intensity on the vertical axis in FIG. 3 indicates the degree of crystallinity.
It is.

As apparent from FIG. 3, the polycrystalline silicon semiconductor (b) provided on the glass substrate which was not heat-treated at a temperature lower than the strain point and the polycrystalline silicon semiconductor (c) provided on the quartz substrate ), The crystallinity of the film of the polycrystalline silicon semiconductor (a) provided on the glass substrate heat-treated at a temperature equal to or lower than the strain point in this example is extremely strong, and its peak is also quartz. It can be seen that it sharply comes out at the same position as the polycrystalline silicon semiconductor provided on the substrate.

Conventionally, in the case of thermal recrystallization, a polycrystalline silicon semiconductor provided on a quartz substrate has been regarded as the best one. Therefore, a polycrystalline silicon semiconductor provided on a glass substrate which has been heat-treated at a temperature lower than its strain point has been used. The sharp peak of the Raman spectrum of the polycrystalline silicon semiconductor (a) film at the same position as the polycrystalline silicon semiconductor (c) provided on the quartz substrate indicates that the glass was heat-treated at a temperature below its strain point. This is considered to mean that the film of the polycrystalline silicon semiconductor (a) provided on the substrate has the characteristics of a pure polycrystalline silicon semiconductor.

That is, while the characteristics of a polycrystalline silicon semiconductor have been impaired by the influence of internal stress in the film in the past, the present embodiment minimizes the generation of internal stress in the polycrystalline silicon semiconductor. As a result, the original characteristics of polycrystalline silicon appeared.

It can also be seen that the peak of the polycrystalline silicon semiconductor (b) provided on the glass substrate which has not been heat-treated is shifted from the position of the polycrystalline silicon. This is because the characteristics of the polycrystalline silicon semiconductor were impaired due to the generation of internal stress.

As described above, the method of heat-treating a glass substrate at a temperature equal to or lower than its strain point not only reduces the shrinkage of the glass substrate in the subsequent heating process, but also provides a heat-recovery provided on the glass substrate. It can be seen that this is an effective means for reducing internal stress and improving crystallinity in the semiconductor to be crystallized.

Further, conventionally, when a polycrystalline silicon semiconductor is produced by thermally recrystallizing an amorphous silicon semiconductor provided on a substrate, it has been considered best to use a quartz substrate as the substrate. According to the data
The measurement result showed that the polycrystalline silicon semiconductor provided on the heat-treated glass substrate according to the embodiment of the present invention had higher crystallinity than the polycrystalline silicon semiconductor provided on the quartz substrate.

Embodiment 2 Hereinafter, an embodiment in which a thermally recrystallized p-SiTFT is manufactured by using the present invention will be described with reference to FIG.

In this embodiment, a heat-recrystallized p-SiTFT is produced on a glass substrate (AN-2 non-alkali glass) (1) which has been heat-treated at a temperature of 610 ° C. for 12 hours.

First, a glass substrate (AN-2 non-alkali glass)
Heat treatment at a temperature of 610 ° C. for 12 hours. The heat treatment method is performed in an electric furnace in an inert gas at atmospheric pressure (N ₂ ) .However, when the heat treatment is performed in an inert gas at an atmospheric pressure or a reduced pressure in which hydrogen is added, the substrate is also washed. Can be done at the same time.

Next, the SiO ₂ film (2) was formed by RF sputtering.
Is formed to a thickness of 200 nm. The film forming conditions are a pressure of 0.5 pa, a temperature of 100 ° C., an RF frequency of 13.56 MHz, and an RF output of 400 W.

An a-Si active layer is formed thereon by RF sputtering.
(3) is deposited to a thickness of 100 nm. The deposition conditions were as follows: pressure 0.5pa,
The temperature is 150 ° C, the RF frequency is 13.56MHz, and the RF output is 400W.

Thereafter, the a-Si film (3) was thermally recrystallized in a nitrogen atmosphere at a temperature of 600 ° C. for 96 hours. The thermal recrystallization is performed in an inert gas (N ₂ ) at atmospheric pressure in an electric furnace.

Device separation patterning was performed on the thermally recrystallized thermally recrystallized p-Si to obtain the shape of (a).

Next, the n ⁺ a-Si film (4) was subjected to PCVD under the following conditions.
The film was formed to a thickness of 50 nm by the method. The deposition condition was a pressure of 6.65.
pa, temperature 350 ° C, RF frequency 13.56MHz, RF output 400W, PH ₃ (5
%): SiH ₄ : H ₂ = 0.2: 0.3: 50 sccm.

Thereafter, gate region patterning is performed (b).
Was obtained.

Next, a gate oxide film (SiO ₂ ) (5) was formed to a thickness of 100 nm by sputtering under the following conditions to obtain the shape of (c). Film formation conditions are pressure 0.5pa, temperature 100 ° C, RF frequency 1
3.56MHz, RF output 400W.

Next, a contact hole was opened and patterning was performed to obtain the shape of (d).

Finally, the aluminum electrode (6) was vacuum-deposited to 300
It was formed to a thickness of nm and patterned to obtain the shape of (e) to complete p-SiTFT.

In the p-SiTFT shown in FIG.
G is a source electrode, G is a gate electrode, and D is a drain electrode. Hereafter, the p-SiTFT fabricated on the heat-treated substrate according to the present embodiment
(a ') and a non-heat-treated glass substrate (Asahi Glass's AN-2
P-SiTFT (b ') fabricated on non-alkali glass) and p-SiTFT (c') fabricated on a quartz substrate in the same manner as in this example.
3 show the results of the three types of comparative evaluations.

As a result of the comparative evaluation, I _D -V _G as shown in FIG.
The characteristics, the relationship between the gate voltage and the field-effect mobility for each substrate shown in FIG. 6, and the substrate dependence of the field-effect mobility as shown in FIG. 7 were obtained.

As is clear from FIG. 5, the p-SiTF of this embodiment
T (a ') is the glass substrate that has not been heat treated (Asahi Glass's AN-2
Drain current (I _D ) -gate voltage (V _G ) characteristics are greatly improved compared to p-SiTFT (b ′) fabricated on non-alkali glass) in the same manner as in this example. It can be seen that the characteristic characteristics approach those of p-SiTFT (c ′) provided on a quartz substrate.

Referring to FIGS. 6 and 7, pS fabricated on a glass substrate (Asahi Glass's AN-2 non-alkali glass) having no field-effect mobility in the same manner as in the present embodiment was used.
p-Si on a quartz substrate, larger than iTFT (b ')
It can be seen that it shows a value similar to the field effect mobility of TFT (c ′).

In this embodiment, the starting material for thermally recrystallizing the a-Si semiconductor provided on the glass substrate is used. However, the present invention uses a non-single-crystal semiconductor other than the a-Si semiconductor on the glass substrate. This is also effective in the case where it is provided.

When the glass substrate is subjected to heat treatment to improve the shrinkage characteristics of the glass substrate, the heat treatment is performed in an inert gas atmosphere under reduced pressure to which hydrogen is added, and the glass substrate is cleaned simultaneously with the heat treatment. This makes it possible to remove adsorbed oxygen that adversely affects the recrystallization of the a-Si semiconductor.

[0056]

According to the present invention, a problem arises in the step of obtaining a polycrystalline semiconductor by thermally recrystallizing a non-single-crystal semiconductor obtained by a gas phase chemical reaction method or a sputtering method. Thus, the problem of shrinkage of the glass substrate could be solved.

The heat treatment is performed on the glass substrate to reduce the shrinkage of the glass substrate during heating, thereby reducing the generation of internal stress generated in the polycrystalline semiconductor provided on the substrate and obtained by thermal recrystallization. Thus, the electrical characteristics of the semiconductor device made of the polycrystalline semiconductor could be improved.

[Brief description of the drawings]

FIG. 1 shows the temperature dependence of the glass shrinkage ratio of a glass substrate manufactured in Example 1.

FIG. 2 shows the time dependence of the glass shrinkage rate of the glass substrate manufactured in Example 1.

FIG. 3 shows Raman spectra of a semiconductor on a glass substrate manufactured in Example 1 and a comparative example.

FIG. 4 illustrates a process for manufacturing a p-SiTFT manufactured in Example 2.

[5] and p-SiTFT prepared in Example 2, shows the I _D (drain current) -V _G (gate voltage) characteristics of the p-SiTFT are comparative examples.

FIG. 6 shows the relationship between the gate voltage and the field-effect mobility of the p-SiTFT fabricated in Example 2 and the p-SiTFT of the comparative example.

FIG. 7 shows the field-effect mobilities of the p-SiTFT fabricated in Example 2 and a p-SiTFT as a comparative example.

[Explanation of symbols]

1 ... glass substrate 2 ... SiO ₂ film 3, ... a-Si active layer 4 ··· n ⁺ a-Si film 5 ... gate oxide film (SiO ₂₎ 6 ... aluminum electrode S ... Source electrode G ... Gate electrode D ... Drain electrode

Claims (11)

[Claims] A heat treatment for shrinking the glass substrate, forming an insulating film made of silicon oxide on the shrunk glass substrate, forming an amorphous semiconductor film on the insulating film made of silicon oxide, A method for manufacturing a semiconductor device, comprising crystallizing a film. A heat treatment for shrinking the glass substrate, forming an insulating film made of silicon oxide on the shrunk glass substrate, forming an amorphous silicon film on the insulating film made of silicon oxide, A method for manufacturing a semiconductor device, comprising crystallizing a film. A heat treatment for the glass substrate, a first insulating film formed on the glass substrate by a sputtering method, a non-single-crystal semiconductor film formed on the first insulating film, A method for manufacturing a semiconductor device, comprising: crystallizing a film; patterning the crystallized non-single-crystal semiconductor film to form an active layer; and forming a second insulating film on the active layer by sputtering. The method for manufacturing a semiconductor device, wherein the first insulating film and the second insulating film are made of the same material, and the active layer is sandwiched between the first insulating film and the second insulating film. . 4. A heat treatment is performed on the glass substrate at a temperature lower than the strain point of the glass substrate, a first insulating film is formed on the glass substrate by a sputtering method, and a non-single-crystal semiconductor is formed on the first insulating film. Forming a film, crystallizing the non-single-crystal semiconductor film, patterning the crystallized non-single-crystal semiconductor film to form an active layer, and forming a second insulating film on the active layer by sputtering. A method of manufacturing a semiconductor device, comprising: shrinking the glass substrate by the heat treatment; and sandwiching the active layer between the first insulating film and the second insulating film. . 5. The method for manufacturing a semiconductor device according to claim 1, wherein the heat treatment is performed in an inert gas of nitrogen. 6. The method for manufacturing a semiconductor device according to claim 1, wherein the heat treatment is performed in an inert gas containing hydrogen. 7. The method for manufacturing a semiconductor device according to claim 1, wherein the glass substrate is made of non-alkali glass. 8. The method according to claim 1, wherein the crystallization is performed by heating. 9. The method for manufacturing a semiconductor device according to claim 1, wherein the insulating film made of silicon oxide is formed by a sputtering method. 10. The method for manufacturing a semiconductor device according to claim 3, wherein the first insulating film and the second insulating film are made of silicon oxide. 11. The strain point is such that the viscosity of glass is 4 × 10 ¹⁴ poi.
5. The method for manufacturing a semiconductor device according to claim 4, wherein the temperature is se.